Understanding a step in a Biot-Savart law problem

In summary, the authors of the book expressed the cross product between the vectors dl and r (unit vector) as dl sin(pi/2 - theta) because in the cross product formula, the angle between the vectors is represented as sin(angle between the vectors) and in the diagram, the angle between the vectors is (π/2-θ). This explains why the authors put pi/2 into the argument of the sin function.
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Anti Hydrogen
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Homework Statement
Biot-Savart law
Relevant Equations
Biot-Savart law
I can't understand intuitively why the authors of the book expressed the cross product between the vectors dl and r (unit vector) as: dl sin(pi/2 - theta); isn't it supposed to be expressed as: dl sin(theta)?? So why did the authors put that pi/2 into the argument of sin function, that's my question, please check the file I attached
 

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Anti Hydrogen said:
Homework Statement:: Biot-Savart law
Relevant Equations:: Biot-Savart law

I can't understand intuitively why the authors of the book expressed the cross product between the vectors dl and r (unit vector) as: dl sin(pi/2 - theta); isn't it supposed to be expressed as: dl sin(theta)?? So why did the authors put that pi/2 into the argument of sin function, that's my question, please check the file I attached
In the cross product formula it is sin(angle between the vectors). In the diagram, the angle between the vectors is (π/2-θ).
 
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  • #3
haruspex said:
In the cross product formula it is sin(angle between the vectors). In the diagram, the angle between the vectors is (π/2-θ).
That makes sense!; I can't believe I didn't consider that! Thanks!
 

1. What is the Biot-Savart law?

The Biot-Savart law is a fundamental equation in electromagnetism that describes the magnetic field generated by a steady current in a wire. It states that the magnetic field at a point is directly proportional to the current, the length of the wire, and the sine of the angle between the wire and the point.

2. How do I apply the Biot-Savart law to a problem?

To apply the Biot-Savart law to a problem, you need to know the current, the length of the wire, and the distance between the wire and the point where you want to calculate the magnetic field. You also need to determine the direction of the current and the angle between the wire and the point. Once you have these values, you can plug them into the equation and solve for the magnetic field.

3. What is the significance of the Biot-Savart law in physics?

The Biot-Savart law is significant because it provides a mathematical relationship between electric currents and magnetic fields. This law is used in many applications, such as calculating the magnetic field of a wire or a solenoid, and understanding the behavior of electric motors and generators.

4. What are some common mistakes when using the Biot-Savart law?

One common mistake when using the Biot-Savart law is forgetting to take into account the direction of the current and the angle between the wire and the point. Another mistake is using the equation for a straight wire when the wire is actually curved. It is important to carefully consider all the variables and their values to ensure an accurate calculation.

5. How does the Biot-Savart law relate to other laws in electromagnetism?

The Biot-Savart law is closely related to other laws in electromagnetism, such as Ampere's law and Gauss's law for magnetism. These laws all describe the relationship between electric currents and magnetic fields, but they have different applications and limitations. The Biot-Savart law is specifically used to calculate the magnetic field due to a steady current, while Ampere's law is used for calculating the magnetic field due to a steady current in a closed loop. Gauss's law for magnetism is used to calculate the magnetic field due to a magnet or a collection of magnets.

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